The long term goal of studies proposed here is to determine the signal transduction mechanisms through which growth factors stimulate hematopoietic proliferation and differentiation. The major goal of this project is to understand the mechanisms through which erythropoietin (Epo) regulates ion channels during erythroid differentiation. Bone marrow aspirates will be performed in the CRC on healthy volunteers. The following specific aims will be addressed: Specific Aim 1: Electrophysiologic characterization of the Epo-regulatable calcium channel. We will employ whole cell attached patch configuration and cell-free inside-out patches to characterize single Ca++ channels and estimate Ca+ channel density. Specific Aim 2: Determination of the signaling mechanisms through which erythropoietin regulates calcium channels. Specific Aim 3: Understanding the mechanisms through which Erythropoietin regulates transcription factors. Some of these mechanisms involve calcium channels.